`a)``(x^2-2x+4)(x+2)-x(x-1)(x+1)+3=0`
`->x^3+2^3-x(x^2-1)+3=0`
`->x^3+8-x^3+x+3=0`
`->x=-8-3`
`->x=-11`
Vậy `S={-11}`
`b)``(x-1)(3-2x)+(2x-1)(x+3)=4`
`->3x-2x^2-3+2x+2x^2+6x-x-3=4`
`->(2x^2-2x^2)+(3x+2x+6x-x)-(3+3)=4`
`->10x-6=4`
`->10x=4+6`
`->x=10/10`
`->x=1`
Vậy `S={1}`